The philosopher Donald Davidson posed the following puzzle. For the most part we understand what others are thinking because we understand the words and sentences that they utter; but we understand what they say only because we know which thoughts their utterances typically express. That makes knowing others’ minds and knowing the meanings of their words and sentences co-dependent. Without knowing both, one cannot grasp either. Davidson called this the problem of radical interpretation. How, he asked, could one overcome this interdependence, to come to know the minds of those whose language one did not speak? Two papers in this issue of Current Biology, by Hobaiter and Byrne and Genty and Zuberbühler, help to answer this question by providing new insights into the relationship of gesture and meaning in chimpanzee and bonobo communication. The problem of radical interpretation is particularly acute when trying to interpret the minds of non-human animals. In the case of humans, we can be relatively confident that their thoughts about the world will be similar to our own, and so use our impressions of a scene as a guide to what they might be saying about it. However, this approach is unreliable where cognitive similarity cannot be assumed. We know that all species of great ape use gestures to communicate with one another, and that these gestures are — as in human language — produced intentionally, causally inefficacious, and addressed to audiences with particular communicative intentions (Figure 1). Because these features are central characteristics of human utterances, ape gestures are meaningful in ways analogous to our own. However, knowing that ape gestures are meaningful is very different from knowing what those gestures mean....